The Symfony\Component\HttpFoundation\Request class provides a mechanism that ensures it does not trust HTTP header values coming from a "non-trusted" client. Unfortunately, it assumes that the remote address is always a trusted client if at least one trusted proxy is involved in the request; this allows a man-in-the-middle attack between the latest trusted proxy and the web server.

The following methods are impacted: getPort(), isSecure(), and getHost(), and getClientIps().